1. Technical Field
The present invention relates to a roll recording material transport device having an assist executing section that executes assist control in which a rotating force is applied to a roll portion of a roll of recording material in the direction of transporting the roll of recording material, and a recording apparatus having such a roll recording material transport device.
2. Related Art
Hereinafter, taking an ink jet printer as an example of a recording apparatus, a description will be made. Some ink jet printers are large-sized ink jet printers that can eject ink onto a large-sized recording material, such as A1 plus size or B0 plus size paper, thereby executing recording. This type of large-sized ink jet printers mainly use a roll of recording material with a width of 24 inches (about 610 mm), 36 inches (about 914 mm), or 44 inches (about 1,118 mm) and a length of 10 m to 45 m. There are used many types of rolls of recording material. They vary in material from paper to film. They range from, for example, resin coated photo paper with high rigidity to plain paper with low rigidity, or from those with a glossy and slippery surface to those with a rough and less slippery surface.
As shown in FIG. 12, roll paper holders 103R and 103L having flange portions 101R and 101L, respectively, are attached to respective ends of the roll of recording material (hereinafter also referred to as roll paper). A spindle 107R is fitted into an engaging hole 105R formed at the center of the roll paper holder 103R. Similarly, a spindle 107L is fitted into an engaging hole 105L formed at the center of the roll paper holder 103L. Engaging projections 109R provided at the base of the spindle 107R engage with engaging step portions 111R of the engaging hole 105R. Similarly, engaging projections 109L provided at the base of the spindle 107L engage with the engaging step portions 111L of the engaging hole 105L. Thus, the power of the spindles 107R and 107L is transmitted through the roll paper holders 103R and 103L, respectively, to the roll paper P.
The spindles 107R and 107L are provided so as to face each other with the roll paper P therebetween. Power is transmitted from a spindle motor 115 through a gear train 113 to the driving side spindle 107R located on the home position side (on the right side of FIG. 12). The driven side spindle 107L located on the other side (on the left side of FIG. 12) is rotatably supported by a support frame 121L with bearings 117 and 119 therebetween.
When the roll paper P is transported by a transport roller (not shown), a desired amount of tension is applied to the roll paper P. To apply the tension, a rotating force is applied to the roll paper P. Types of control for applying the rotating force include tension control shown in FIG. 13A and assist control shown in FIG. 13C. In the tension control, to apply a desired amount of tension to the roll paper P, a motor toque (spindle motor 115) is applied so that a rotating force is applied to the roll paper P in a rewinding direction B, or the opposite direction from the pulling out direction (the direction of transporting the roll paper P) A. However, in the case of the tension control, the tension to be applied to the roll paper P needs to be set equal to or more than the friction torque that is the mechanical load of the support mechanism that supports the roll paper P. Therefore, the tension control cannot be applied to a roll paper P for which a high tension cannot be set, for example, a roll paper P with a slippery surface.
In contrast, in the assist control, a motor toque (spindle motor 115) is applied so that a rotating force is applied to the roll paper P in a direction A such that the transport of the roll paper P is assisted. In the case of the assist control, the tension applied to the roll paper P can be reduced less than the friction torque that is the mechanical load of the support mechanism that supports the roll paper P. Therefore, the assist control can also be applied to a roll paper P with a slippery surface.
However, in FIG. 12, when the mechanical load L1 based mainly on the frictional force M1 between the driving side spindle 107R and the engaging hole 105R in the driving side roll paper holder 103R is larger than the mechanical load L2 based on the frictional force 2M2 between the driven side spindle 107L and the bearings 117 and 119, a state can occur in which the engaging projections 109R are out of contact with the engaging step portions 111R as shown in FIG. 13B. That is, depending on whether or not the mechanical load L1 is larger than the mechanical load L2, the engaging projections 109R can exist within the areas between adjacent engaging step portions 111R, and the engagement of the driving side spindle 107R with the driving side roll paper holder 103R in the assist direction can become uncertain or unstable, and the torque applied for the assist control can also become unstable.
To the spindles 107R and 107L, a spring clutch (not shown) is attached, or a torque limiter such as that shown in JP-A-2007-290866 is connected. By the action of the spring clutch or torque limiter, a constant torque serving as a resistance to transport is applied to the roll paper P, and a tension is applied to the roll paper P between the transport roller that guides the roll paper P to the recording position and the roll portion. However, the tension of the roll paper P generated by the action of the spring clutch or torque limiter varies with changes in the roll diameter of the roll paper P. This affects the accuracy of feeding the roll paper P and reduces the recording quality.